DL06 & DL08 ECU System – Bosch EDC7UC31 Wiring, Sensors, and Diagnostic Guide

DL06 & DL08 ECU System – Bosch EDC7UC31 Control, Harness, and Diagnostic Guide

This article explains the ECU (Engine Control Unit) used on Doosan DL06 and DL08 / DV11 Common Rail engines. It covers ECU hardware (Bosch EDC7UC31), harness layout, sensor and injector connections, and ECU control functions for engine starting, preheating, after-heating, limp-home, and emergency stop. Use this as a technician-level reference for wiring checks, diagnostics, and understanding ECU logic.

1. ECU Hardware Overview (Bosch EDC7UC31)

The DL06 / DL08 Common Rail system uses a Bosch EDC7UC31 ECU with special software for Doosan engines. The ECU is the central controller for fuel injection, rail pressure, and several auxiliary functions such as preheating, after-heating, limp-home, and emergency stop. Understanding the external connectors and internal control logic is essential for proper diagnosis and repair.

Doosan DL06 ECU diagram showing injector connector, vehicle connector, engine connector and atmospheric pressure sensor

On the ECU housing you will typically find:

Injector connector: Connects the ECU to all injector solenoids via the injector harness.
Engine connector: Connects engine sensors such as crank, cam, water temp, fuel temp, boost pressure, and rail pressure.
Vehicle connector: Connects to the vehicle side (EPOS, LCD panel, power supply, CAN, etc.).
Atmospheric pressure sensor: Often integrated in the ECU body for altitude compensation.

Some versions show an ATM sensor (not used) label on the ECU, which indicates a placeholder or unused port in that specific application. Always match the connector layout and part number with the correct service manual for the engine.

2. ECU Mounting, Tightening Order, and Torque

The ECU must be mounted correctly to avoid vibration damage, water ingress, or internal board failure. The tightening sequence and torque are specified to protect the ECU housing and ensure an even seal.

Doosan ECU tightening order and torque diagram showing 8 bolt sequence for common rail system

Tightening order: 8 bolts numbered 1 to 8, following the sequence in the diagram (typically cross pattern).
Tightening torque: 1 ± 0.2 kg·m (always convert and confirm in N·m if required by your torque wrench).

Always tighten the ECU mounting bolts gradually in stages, following the specified sequence. Over-tightening or uneven tightening can stress the housing and internal PCB, leading to long-term reliability issues.

3. DL06 Engine Connector Harness (Sensor Side)

The engine connector harness links the ECU to key engine sensors. A clean, correct signal from each sensor is essential for accurate injection timing, fuel quantity control, and protection functions.

DL06 engine connector harness diagram showing crankshaft sensor, camshaft sensor, rail pressure sensor, fuel temperature, oil pressure, boost pressure and coolant temperature sensors

Typical sensors connected via the DL06 engine connector harness:

Crankshaft speed sensor (CRS): Provides engine RPM and position reference.
Camshaft speed sensor (CAS): Cylinder recognition and timing synchronization.
Common rail pressure sensor (RPS): Feedback of actual rail pressure to the ECU.
Fuel temperature sensor (FTS): Used to correct injection quantity based on fuel density.
Oil pressure sensor (OPTS): Monitors engine lubrication and can trigger protection modes.
Boost pressure sensor (BPTS): Measures intake pressure for load and smoke control.
Water temperature sensor (CTS): Coolant temperature for warm-up, preheating, and protection logic.

When diagnosing ECU-related issues, checking this harness for pin fitment, corrosion, damage, or incorrect pin-outs is often the first practical step.

4. DL08 & DV11 Engine Connector Harness (Sensor Mapping)

The DL08 & DV11 engines use a similar concept, but the harness drawing shows more detailed pin mapping and wire identification. This is crucial when tracing faults or verifying continuity.

Doosan common rail ECU front and back view showing vehicle connector, engine connector and injector connector

The diagram typically lists, for each sensor:

Pin numbers at the ECU connector.
Wire colors or codes (P/B, N, etc.).
Shielded lines for sensitive signals such as crank and cam sensors.

Use these pin references when:

Measuring sensor supply voltage (e.g., 5 V reference).
Checking ground continuity between sensor and ECU.
Verifying signal output (e.g., frequency from speed sensors, voltage from pressure sensors).

5. Injector Connector Harness (DL06, DL08 & DV11)

The injector harness connects the ECU to each injector solenoid. A stable power and clean control signal are vital for precise injection events. Faults here can cause misfire, rough running, or rail pressure errors.

DL08 and DV11 engine connector harness diagram with wiring for rail pressure, boost pressure, fuel temperature, coolant temperature, crankshaft and camshaft sensors

For DL06, the injector harness diagram shows:

ECU side connector: Main connection from ECU injector output pins.
Fuel metering unit (MEU / FMU): Often included in the same harness.
Intermediate injector connectors: Junction between main harness and each cylinder injector.
Cylinders #1 to #6: Clearly labeled to avoid cross-connection.

DL06 injector connector harness diagram showing ECU side, fuel metering unit and injector connectors for cylinders 1 to 6

For DL08 & DV11, the injector harness diagram details:

ECU connector pins assigned to each injector (CYL 1 to CYL 6).
Dual wires per injector (typically one power, one control/ground side switching).
Pin layouts for intermediate connectors to each cylinder.

This information is particularly useful when checking:

Injector resistance at the ECU connector (to avoid opening harness in harsh environments).
Short to ground or short to power on injector circuits.
Crossed injectors after harness or engine repair.

6. ECU Control Functions – Starting, Preheating, After-Heating

The ECU uses multiple sensor inputs to decide fuel quantity, injection timing, and preheating/after-heating strategies, especially during cold starts. Several diagrams explain this logic in detail.

6.1 Engine Starting

During engine start, the ECU:

Senses coolant, fuel, and intake air temperature to calculate the correct starting fuel quantity.
Uses the crankshaft speed sensor to measure engine RPM on the flywheel housing.
Drives the injectors with a starting-specific injection strategy (longer duration, adjusted timing).

ECU control diagram showing coolant, fuel and air temperature inputs with engine RPM for starting and preheating functions

The ECU decides the optimal fuel quantity for starting based on temperature and engine speed to reduce smoke, improve start quality, and protect components.

6.2 Preheating and After-Heating

For cold conditions, the ECU manages preheating and after-heating:

Preheating: Active with key ON; ECU reads coolant, fuel, and air temp to decide if heating is needed.
Warning lamp: Illuminated during preheating; time depends on coolant temperature.
After-heating: May continue heating after engine start (typically no warning lamp) to stabilize combustion.
Voltage condition: Preheating/after-heating is disabled if battery voltage is below the specified limit (e.g., 11–12 V, depending on slide/version).

In practice, if heaters are not working:

Check coolant temperature sensor reading – if it shows high temp while engine is cold, heating will not activate.
Check battery voltage – low voltage can disable the heating function.
Verify air heater relay and wiring controlled by ECU.

7. ECU After-Heating and Limp-Home Control

ECU control diagram showing after heating logic and limp home mode at fixed 1000 RPM when EPOS or LCD panel fails

7.1 After-Heating Function

After the engine has started, the ECU may still apply after-heating:

Inputs: Coolant temp, fuel temp, air temp, and engine running signal.
Output: Air heater control from ECU (no warning lamp in this phase).
Decision: ECU calculates how long after-heating is needed based on coolant temperature.
Voltage condition: If battery voltage is below about 12 V, heating is disabled to protect the battery.

7.2 Limp-Home Function

The limp-home function is designed to keep the engine running at a safe fixed speed (e.g., ~1000 RPM) if certain control units lose communication.

LCD panel / EPOS failure: If the ECU detects no signal or a failure from these units, it may enter limp-home mode.
Fixed engine speed: ECU controls fuel injection to hold a constant RPM so the machine can be moved to a safe area or workshop.
Limited power: Not suitable for normal work, but enough to prevent towing in many cases.

When limp-home mode is active, always check:

Communication lines between ECU, EPOS, and display (CAN or dedicated lines).
Power and grounds to EPOS and LCD panel.
Fault codes stored in the ECU with the appropriate diagnostic tool.

8. ECU Emergency Stop Function

ECU emergency stop diagram showing emergency stop signal cutting fuel injection

The ECU also handles the emergency stop function:

Emergency engine stop signal: Typically from an emergency switch or safety system.
ECU reaction: Immediately cuts fuel injection to stop the engine.
Engine running signal: Confirms whether the engine is still turning; ECU ensures injection remains off until a safe reset condition is met.

If the engine cannot be restarted after an emergency stop event:

Check the emergency stop circuit and switch reset position.
Verify input signal at the ECU (high/low status as specified in the manual).
Scan for active fault codes that may lock out injection until cleared.

9. Technician Notes and Diagnostic Tips for DL06 / DL08 ECUs

When dealing with ECU-related issues on DL06, DL08, or DV11 Common Rail engines, use a structured diagnostic approach combining wiring diagrams, harness layouts, and ECU control logic.

Always inspect harnesses first: Look for damaged insulation, oil contamination, pin corrosion, or poor pin fit.
Use pin maps: The engine and injector connector harness diagrams let you test sensors and injectors directly from the ECU plug.
Check power and ground: Ensure ECU main power, ignition feed, and grounds are clean and within spec before suspecting ECU failure.
Verify sensor readings: Compare live data (coolant temp, fuel temp, air temp, rail pressure, RPM) with actual engine conditions.
Understand ECU logic: Use the starting, preheating, after-heating, limp-home, and emergency stop diagrams to interpret why the ECU is acting in a certain way.
Use proper diagnostic tools: For Doosan systems, use the approved diagnostic software and interface for reading codes and performing tests.

Conclusion

The DL06 and DL08 / DV11 ECUs based on Bosch EDC7UC31 form the core of the Common Rail control system. By understanding the hardware layout, sensor and injector harnesses, and ECU control functions for starting, heating, limp-home, and emergency stop, technicians can perform accurate diagnostics and avoid unnecessary ECU replacement. Always combine wiring diagrams, pinouts, and live ECU data when troubleshooting for the most efficient and professional results.

Doosan-dl06-dl08-common-rail-fuel-system-guide.